APS-Journal Jan 2017

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10 Journal of the American Pomological Society
stock shank diameter (5 cm below the graft
union), two perpendicular graft union diam-
eter measurements at the widest part of the
graft union, scion stem diameter (5 cm above
the graft union and scion height above the
graft union.
Sample Preparation. In November, trees
were harvested mechanically using standard
commercial practices and kept in cold stor-
age for later graft strength analysis. When
ready for analysis, trees were topped to an
overall length of about 70 cm and the roots,
leaves and lateral shoots were removed. Trees
were then bundled according to tree number,
packed in ice and transported to a laboratory
at Utah State University in Logan, Utah.
Break Strength Testing. In the laboratory,
each specimen was loaded to failure using a
3-point bend apparatus with a 16 cm sepa-
ration (Fig. 1). The apparatus was used in
conjunction with a Bench Testing Machine
(Tinius Olsen H50KS, Horsham, PA) oper-
ating in compression mode. The tests were
performed with a fixed strain rate (25 cm/
min) as per the ASTM Standard D790 and
D7264, which are commonly used for testing
of flexural strength of polymer composites
and concrete (ASTM, 2010; ASTM, 2015). A
pre-load condition of 10 N was used to bring
the crosshead into contact with the speci-
men at a constant rate of 50 cm/min. Force
measurements were acquired through the
equipment software (Tinius Olsen Test Navi-
gator) at 1-second intervals throughout the
measurement until a failure condition was
achieved. Upon achieving the failure condi-
tion, the fracture strength was obtained from
the data based on the geometry of the 3-point
Table 1. Plant growth regulator treatments used in 2014. The commercial formulations, concentrations,
application method, and number of applications are shown. ACC provided as experimental formulation from
Valent BioSciences (Libertyville, IL).
Chemical Name Trade Name Concentration Application # of
(mg·L-1 ) method Applications
Untreated control – NA NA NA
Painted control Water+Paint 50:50 (v) Graft Paint 1
NAA Fruitone ®N 20 Foliar Spray 1
NAA Fruitone®N 20 Foliar Spray 2
NAA Fruitone®N 250 Graft Paint 1
NAA Fruitone®N 250 Graft Paint 2
IBA Water+Ethanol 2600 Graft Paint 1
IBA Water+Ethanol 2600 Graft Paint 2
ACC Experimental 200 Foliar Spray 1
ACC Experimental 200 Foliar Spray 2
ACC Experimental 2500 Graft Paint 1
ACC Experimental 2500 Graft Paint 2
Ethephon Ethrel® 2500 Graft Paint 1
Ethephon Ethrel® 2500 Graft Paint 2
S-ABA ProTone® SG 320 Foliar Spray 1
S-ABA ProTone® SG 320 Foliar Spray 2
S-ABA ProTone® SG 4000 Graft Paint 1
S-ABA ProTone® SG 4000 Graft Paint 2
BA MaxCel® 2500 Graft Paint 1
BA MaxCel® 2500 Graft Paint 2
GA4+7 ProVide® 2500 Graft Paint 1
GA4+7 ProVide® 2500 Graft Paint 2